Abstract

Ultraviolet light was measured at four channels (305, 311, 318,
and 332 nm) with a precision filter radiometer (UV-PFR) at Arosa,
Switzerland (46.78°, 9.68°, 1850 m above sea level),
within the instrument trial phase of a cooperative venture of the Swiss
Meteorological Institute (MeteoSwiss) and the
Physikalisch-Meteorologisches Observatorium Davos/World Radiation
Center. We retrieved ozone-column density data from these direct
relative irradiance measurements by adapting the Dobson standard method
for all possible single-difference wavelength pairs and one
double-difference pair (305/311 and 305/318) under conditions
of cloud-free sky and of thin clouds (cloud optical depth <2.5 at
500 nm). All UV-PFR retrievals exhibited excellent agreement with
those of collocated Dobson and Brewer spectrophotometers for data
obtained during two months in 1999. Combining the results of the
error analysis and the findings of the validation, we propose to
retrieve ozone-column density by using the 305/311 single difference
pair and the double-difference pair. Furthermore, combining both
retrievals by building the ratio of ozone-column density yields
information that is relevant to data quality control. Estimates of
the 305/311 pair agree with measurements by the Dobson and Brewer
instruments within 1% for both the mean and the standard deviation of
the differences. For the double pair these values are in a range up
to 1.6%. However, this pair is less sensitive to model
errors. The retrieval performance is also consistent with
satellite-based data from the Earth Probe Total Ozone Mapping
Spectrometer (EP-TOMS) and the Global Ozone Monitoring Experiment
instrument (GOME).

G. M. B. Dobson, D. N. Harrison, “Measurement of
the amount of ozone in the Earth’s atmosphere and its relation to other
geophysical conditions,” Proc. R. Soc. London Ser. A 110, 660–693
(1926).
[CrossRef]

A. Hahne, A. Lefebvre, J. Callies, B. Christensen,
“GOME—The development of a new instrument,” ESA Bull. 83 (European Space
Agency Directorate for Observation of the Earth and Its Environment,
European Space Research and Technology Centre, Noordwijk, The Netherlands,
1995).

1929 (1)

1926 (1)

G. M. B. Dobson, D. N. Harrison, “Measurement of
the amount of ozone in the Earth’s atmosphere and its relation to other
geophysical conditions,” Proc. R. Soc. London Ser. A 110, 660–693
(1926).
[CrossRef]

Callies, J.

A. Hahne, A. Lefebvre, J. Callies, B. Christensen,
“GOME—The development of a new instrument,” ESA Bull. 83 (European Space
Agency Directorate for Observation of the Earth and Its Environment,
European Space Research and Technology Centre, Noordwijk, The Netherlands,
1995).

Christensen, B.

A. Hahne, A. Lefebvre, J. Callies, B. Christensen,
“GOME—The development of a new instrument,” ESA Bull. 83 (European Space
Agency Directorate for Observation of the Earth and Its Environment,
European Space Research and Technology Centre, Noordwijk, The Netherlands,
1995).

Dobson, G. M. B.

G. M. B. Dobson, D. N. Harrison, “Measurement of
the amount of ozone in the Earth’s atmosphere and its relation to other
geophysical conditions,” Proc. R. Soc. London Ser. A 110, 660–693
(1926).
[CrossRef]

Hahne, A.

A. Hahne, A. Lefebvre, J. Callies, B. Christensen,
“GOME—The development of a new instrument,” ESA Bull. 83 (European Space
Agency Directorate for Observation of the Earth and Its Environment,
European Space Research and Technology Centre, Noordwijk, The Netherlands,
1995).

Harrison, D. N.

G. M. B. Dobson, D. N. Harrison, “Measurement of
the amount of ozone in the Earth’s atmosphere and its relation to other
geophysical conditions,” Proc. R. Soc. London Ser. A 110, 660–693
(1926).
[CrossRef]

Lantz, K.

Lefebvre, A.

A. Hahne, A. Lefebvre, J. Callies, B. Christensen,
“GOME—The development of a new instrument,” ESA Bull. 83 (European Space
Agency Directorate for Observation of the Earth and Its Environment,
European Space Research and Technology Centre, Noordwijk, The Netherlands,
1995).

Proc. R. Soc. London Ser. A (1)

G. M. B. Dobson, D. N. Harrison, “Measurement of
the amount of ozone in the Earth’s atmosphere and its relation to other
geophysical conditions,” Proc. R. Soc. London Ser. A 110, 660–693
(1926).
[CrossRef]

A. Hahne, A. Lefebvre, J. Callies, B. Christensen,
“GOME—The development of a new instrument,” ESA Bull. 83 (European Space
Agency Directorate for Observation of the Earth and Its Environment,
European Space Research and Technology Centre, Noordwijk, The Netherlands,
1995).

Figures (9)

Zenith transmittance of ozone absorption in the UV
through the MLS (Ω = 331.7 DU) computed with
modtran 3.7. Resolution is set to 5 cm-1
(≈0.05 nm, depending on wavelength). Superimposed are the
spectral responses of the four UV-PFR channels.

Scatterplot of ozone-column density retrievals of the
UV-PFR 305/311 and the Brewer72, as measured in Arosa (1850 m
asl) from mid-July 1999 to mid-September 1999. UV-PFR data were
averaged over 20-min intervals.

Mean (top) and standard deviation (bottom) of
ozone-column density difference, UV-PFR minus Dobson or
Brewer. Results for each UV-PFR pair are averaged and are given for
all data and for a reduced data set when no clouds obscured the Sun.

Variation of daily means of ozone-column density as
measured at Arosa (1850 m asl) with the Dobson101 spectrometer and
the UV-PFR with the single-difference pair 305/311 and the
double-difference pair. In addition, satellite-based EP-TOMS and
GOME overpass data are plotted for the selected dates.

modtran simulation of the aerosol term in the
ozone retrievals for the single-difference pair and the
double-difference pair, from different built-in aerosol profiles along
a vertical path to space (0° SZA). Neglecting the aerosol
term leads to an overestimation (underestimation) for the single
pairs (double pair).

Distribution of aerosol optical depth measured at 500 nm
for Arosa during the period from mid-July to mid-September
1999. The AOD values of the modtran simulations for the
tropospheric case (×) and the rural case with visibility of 23 km
(+) are superimposed. stdev, Standard deviation.

a Measured ozone-column density minus true
ozone-column density.b The SO2 and aerosol terms are
neglected. All data are given in Dobson units, rounded to 0.5 DU.c For the algorithm the model error is <0.5 for
all pairs; that for the cirrus clouds is -0.5–0.5; that for the
passband is <1.0.d According to the range of measured data.e Invariant temperature-weighted ozone-absorption
coefficients α1 for Ω = 300 DU.f Pressure <0.5 for all pairs.g For SZA = 25° (air mass, ≈1.10).h For Ω = 300 DU.

Table 3

Total Ozone Statistics of Measurements Performed at Arosa
(1850 m asl) of UV-PFR, Dobson, and Brewer Data from Mid-July 1999
to Mid-September 1999a

a Data of instrument A are averaged over
20-min intervals centered at the time of measurement of instrument
B. All relative values are given with respect to
instrument B.b Standard deviation.c 10-min intervals instead of 20-min intervals.

Table 4

Total Ozone Statistics of Measurements from UV-PFR Data
Obtained at Arosa (1850 m asl) and Satellite Overpass Data for
Arosaa

a UV-PFR data are averaged over a 1-h
interval centered at the measurement time of the EP-TOMS or at 10:00 UT
for GOME data. All relative values are given with respect to
instrument B.b Standard deviation.

Tables (4)

Table 1

Manufacturer Specifications of Central Wavelength and
Bandwidth for the Nominal UV-PFR Channels of the Instrument Installed
at Arosa

Channel (nm)

Effective Central Wavelength λi (nm)

Bandwidth Δλi (nm)

305

305.30

1.12

311

311.20

1.17

318

317.40

1.25

332

332.40

1.25

Table 2

Error Contribution of Ozone Retrievals in the
UVa
for Ω = 300 DU and
SZA = 25° for Cloud-Free Sky and Cirrus Clouds with a
Climatological Mean for
NO
2
b

a Measured ozone-column density minus true
ozone-column density.b The SO2 and aerosol terms are
neglected. All data are given in Dobson units, rounded to 0.5 DU.c For the algorithm the model error is <0.5 for
all pairs; that for the cirrus clouds is -0.5–0.5; that for the
passband is <1.0.d According to the range of measured data.e Invariant temperature-weighted ozone-absorption
coefficients α1 for Ω = 300 DU.f Pressure <0.5 for all pairs.g For SZA = 25° (air mass, ≈1.10).h For Ω = 300 DU.

Table 3

Total Ozone Statistics of Measurements Performed at Arosa
(1850 m asl) of UV-PFR, Dobson, and Brewer Data from Mid-July 1999
to Mid-September 1999a

a Data of instrument A are averaged over
20-min intervals centered at the time of measurement of instrument
B. All relative values are given with respect to
instrument B.b Standard deviation.c 10-min intervals instead of 20-min intervals.

Table 4

Total Ozone Statistics of Measurements from UV-PFR Data
Obtained at Arosa (1850 m asl) and Satellite Overpass Data for
Arosaa

a UV-PFR data are averaged over a 1-h
interval centered at the measurement time of the EP-TOMS or at 10:00 UT
for GOME data. All relative values are given with respect to
instrument B.b Standard deviation.